The present invention relates to a wastewater treatment method and apparatus. For example, the present invention relates to an energy-saving wastewater treatment method and apparatus by which wastewater containing dimethylformamide, which is a toxic chemical substance, can be completely decomposed by using microorganisms. Further, the present invention relates to a wastewater treatment method and apparatus using a biological treatment tank having a submerged membrane and a foaming tank in combination.
Since the PRTR (Pollutant Release and Transfer Register) Law (the Law Concerning Reporting, etc. of Releases to the Environment of Specific Chemical Substances and Promoting Improvements in Their Management) came into operation in April 2001, much attention has been paid to the amount of releases of toxic chemical substances to environment.
Furthermore, today, when addressing to global environment is the most important issue, energy saving in wastewater treatment equipment is also an important theme.
Against such a backdrop, dimethylformamide used in a semiconductor factory has been designated as a toxic chemical substance (Class-1 designated chemical substance) by the PRTR Law, and thus thorough control and reduction of an amount of dimethylformamide release are being required. Wastewater containing dimethylformamide has been conventionally subjected to incineration due to its biological toxicity. In the case of incineration, however, a system with low environmental load cannot be provided since heavy oil or the like is used as an incineration fuel and wastewater needs to be transported to an incineration plant.
Furthermore, as a conventional technique, the technique described in Japanese Patent Laid-Open Publication No. 8-99092 has been proposed. This conventional technique relates to a wastewater treatment apparatus in which wastewater containing high-concentration organic matter is treated by increasing a microorganism concentration. That is, a vinylidene-chloride filler and a submerged membrane (referred to as a membrane filter) are installed in a catalytic oxidation tank as a bioreactor, and wastewater is treated by increasing the microorganism concentration. In this technique, however, no energy saving measure is taken. Specifically, no energy saving measure is taken for a blower, which has high power consumption as equipment. Furthermore, it is not disclosed in this technique that dimethylformamide as a toxic substance can be completely decomposed by a catalytic oxidation tank maintaining a high concentration of microorganisms.
Furthermore, as another conventional technique, the technique described in Japanese Patent Laid-Open Publication No. 9-70599 has been proposed. This conventional technique also relates to a wastewater treatment apparatus in which wastewater containing high-concentration organic matter is treated by increasing a microorganism concentration as in the case of the aforementioned apparatus described in Japanese Patent Laid-Open Publication No. 8-99092. In this conventional technique, a vinylidene-chloride filler and a submerged membrane (referred to as a membrane filter) are installed in a catalytic oxidation tank as a bioreactor, and wastewater is treated by increasing the microorganism concentration. However, no energy saving measure is taken in this technique, either. Specifically, no energy saving measure is taken for a blower, which has high power consumption as equipment. Furthermore, it is not disclosed that dimethylformamide as a toxic substance can be completely decomposed by a catalytic oxidation tank maintaining a high concentration of microorganisms.
Furthermore, a wastewater treatment apparatus shown in FIG. 16 can be mentioned as another conventional technique. In this FIG. 16, reference numeral 101 denotes an aeration tank, in which microorganisms are propagated, and wastewater is introduced thereinto. In this aeration tank 101, air supplied from a blower 102 is discharged from a diffusing pipe 103 to perform aeration by agitation in the aeration tank 101, and thus oxygen in the air is supplied into the aeration tank 101. Consequently, aerobic microorganisms are propagated in the aeration tank 101 to treat organic matter.
Subsequently, the wastewater biologically treated in this aeration tank 101 is introduced into a sedimentation tank 104 and separated into a solid and a liquid by sedimentation. The sedimentation tank 104 is equipped with a gathering device 105 and a sludge returning pump 106 for returning sludge sedimented in the sedimentation tank 104 to the aeration tank 101. This sludge from the sludge returning pump 106 is partly dehydrated in a sludge treatment process. Electrical energy for operating the blower 102 is required in this wastewater treatment apparatus, but no rational energy saving method has been provided for this energy consumption.
Furthermore, a wastewater treatment apparatus shown in FIG. 17 can be mentioned as another conventional technique. In FIG. 17, reference numeral 110 denotes a catalytic oxidation tank, in which microorganisms are propagated and a filler 109 is filled, and wastewater is introduced thereinto. In this catalytic oxidation tank 110, air supplied from a blower 102 is discharged from a diffusing pipe 103 to perform contact aeration by agitation in the catalytic oxidation tank 110, and thus oxygen from the air is supplied into the catalytic oxidation tank 110. Consequently, organic matter is treated by propagating aerobic microorganisms in the catalytic oxidation tank 110.
Subsequently, the wastewater biologically treated in this catalytic oxidation tank 110 is introduced into a sedimentation tank 104 and separated into a solid and a liquid by sedimentation. This sedimentation tank 104 is equipped with a gathering device 105 and a sludge returning pump 106 for returning sludge sedimented in the sedimentation tank 104 to the catalytic oxidation tank 110. This sludge from the sludge returning pump 106 is partly dehydrated in a sludge treatment process. Electrical energy for operating the blower 102 is also required in this wastewater treatment apparatus, but no rational energy saving method has been provided for this energy consumption of the blower 102.
Furthermore, as another conventional technique, a wastewater treatment apparatus shown in FIG. 18 has been proposed. In FIG. 18, reference numeral 115 denotes a rotating disc tank, in which microorganisms are propagated, and wastewater is introduced thereinto. In this rotating disc tank 115, a rotating disc 117 is driven by a motor 116 to be rotationally moved in water and air. Consequently, oxygen is supplied, and thus organic matter is treated by propagating aerobic microorganisms on a surface of the disc 117.
Subsequently, the wastewater biologically treated in this rotating disc tank 115 is introduced into a sedimentation tank 104 and separated into a solid and a liquid by sedimentation. This sedimentation tank 104 is equipped with a gathering device 105 and a sludge returning pump 106 for returning sludge sedimented in the sedimentation tank 104 to the rotating disc tank 115. This sludge from the sludge returning pump 106 is partly dehydrated in a sludge treatment process. Electrical energy for driving the rotating disc 117 is also required in this wastewater treatment apparatus, but there has been provided no wastewater treatment apparatus with which initial costs can be reduced and energy saving can be achieved.
Furthermore, examples of other conventional techniques include those described in Japanese Patent Laid-Open Publication Nos. 1-60371, 1-63372, 1-135595, 1-148398, 2-72864, 2-72865, 3-217298, 5-64796, 5-64797 and 5-269488.
These conventional techniques all relate to a method of decomposing dimethylformamide by specific microorganisms. However, it is difficult to manage wastewater treatment equipment so as to culture specific microorganisms in a biological treatment tank, in which other various bacteria are mixed, and it is difficult to manage operations so as to maintain specific microorganisms for a continuous long time.
As described above, wastewater containing dimethylformamide as a toxic chemical substance is generally disposed by incineration, but a specific problem arises that incineration costs are high. Furthermore, in an era of conservation of global environment, a method of incinerating wastewater by using heavy oil is not regarded as an energy-saving disposal method. Furthermore, there is a decomposition method by specific microorganisms, but a problem arises that advanced technology is required for operation management or the like to culture only specific microorganisms due to influence of other various bacteria. That is, a method has been required in which wastewater is treated not by specifying microorganisms, but by using aggregation of various microorganisms such as activated sludge.
However, the activated sludge method is a treatment method using aggregation of various microorganisms, but a microorganism concentration in MLSS (Mixed Liquor Suspended Solid) is low at 3000-4000 ppm. Therefore, dimethylformamide as a toxic chemical substance cannot be completely decomposed. The microorganism concentration in MLSS in this activated sludge method is generally 3000-4000 ppm.
Conventionally, when wastewater containing dimethylformamide as a toxic chemical substance is treated, incineration has been performed since incineration is mentioned in a xe2x80x9cChemical Substance etc. Safety Data Sheetxe2x80x9d of a chemical manufacturer, and complete decomposition of dimethylformamide has been impossible in a general microorganism treatment system.
Accordingly, an object of the present invention is to provide a wastewater treatment method and apparatus in which energy to be consumed can be saved and easy management can be achieved by completely decomposing toxic chemical substances such as dimethylformamide by using unlimited microorganisms.
In order to achieve the above object, there is provided a wastewater treatment method comprising steps of treating wastewater by introducing the wastewater into a biological treatment tank,
introducing the treated water from the biological treatment tank into a sedimentation tank, separating sludge generated in this sedimentation tank by sedimentation, treating this sedimented sludge by introducing the sludge into a foaming tank having a function of generating air bubbles, and
returning the sludge treated in the foaming tank to the biological treatment tank.
Also, there is provided a wastewater treatment apparatus comprising a biological treatment tank, in which wastewater is treated by organisms,
a sedimentation tank, into which the treated water from the biological treatment tank is introduced and in which generated sludge is separated by sedimentation, and
a foaming tank, into which the sludge sedimented in the sedimentation tank is introduced and which has a function of generating air bubbles and treats and returns the sludge to the biological treatment tank.
According to the wastewater treatment method of the present invention and a wastewater treatment apparatus of one embodiment, wastewater can be treated by novel action by a foaming tank in comparison with a treatment method solely using a biological treatment tank. That is, wastewater can be treated by action achieved by combining (1) sole action of the biological treatment tank and (2) action of the foaming tank. Specific action by this foaming tank includes a supply of dissolved oxygen to wastewater under a favorable condition in shallow water depth and oxidation by bubbled air (micro air).
For example, while the foaming tank has a water depth of about 1 m, the aeration tank has a water depth of about 4-5 m. When the water tank is deep, pressure loss of the blower is increased, and electric power consumption is increased.
In one embodiment of the present invention, the biological treatment tank is any one of an aeration tank, catalytic oxidation tank or rotating disc tank or a combination thereof.
In one embodiment of the present invention, the biological treatment tank is any one of an aeration tank, catalytic oxidation tank or rotating disc tank or a combination thereof.
According to the above embodiment, the biological treatment tank is any one of an aeration tank, catalytic oxidation tank or rotating disc tank or a combination thereof. Therefore, according to the above wastewater treatment apparatus and method, a novel effect by the foaming tank can be added to an effect obtained by solely using a conventional aeration tank, catalytic oxidation tank or rotating disc tank.
Here, an aeration tank and a catalytic oxidation tank are different in that a tank containing a filler to be brought in contact with wastewater is referred to as a catalytic oxidation tank and a tank without this filler is referred to as an aeration tank.
In one embodiment of the present invention, the wastewater is wastewater containing organic matter.
In the wastewater treatment method according to this embodiment, since the wastewater is wastewater containing organic matter, this organic matter can be treated by action achieved by combining (1) action of a sole biological treatment tank and (2) action of a foaming tank. Specifically, wastewater can be treated by a system in which (1) oxidation is performed by aerobic microorganisms in the biological treatment tank and (2) sufficient oxygen can be supplied to microorganisms with low electrical energy due to micro air in the foaming tank. That is, energy saving can be achieved.
Also, there is provided a wastewater treatment method comprising steps of introducing wastewater into a biological treatment tank equipped with a submerged membrane and treating the wastewater,
introducing sludge generated in the biological treatment tank into a foaming tank having a function of generating bubbles and treating the sludge, and
returning the sludge treated in the foaming tank to the biological treatment tank.
Also, there is provided a wastewater treatment apparatus which comprises a biological treatment tank having a submerged membrane, in which wastewater is treated by living organisms, and
a foaming tank, into which sludge sedimented in the biological treatment tank is introduced and which has a function of generating air bubbles and treats and returns the sludge to the biological treatment tank.
In the wastewater treatment method and apparatus according to the above constitution, since a submerged membrane is installed in the biological treatment tank (for example, an aeration tank or catalytic oxidation tank), propagated microorganisms can be maintained in this biological treatment tank, and microorganisms can be concentrated to a high concentration by the submerged membrane.
Thus, since microorganisms can be concentrated to a high concentration by the submerged membrane, toxic chemical substances mainly including organic matter, which can be hardly treated by microorganisms conventionally, can be treated by microorganisms. This is because high-concentration microorganisms reduce influence of toxic chemical substances and hence the microorganisms have stronger ability to decompose the toxic chemical substances.
In one embodiment of the present invention, the wastewater is organic wastewater containing dimethylformamide.
According to the above wastewater treatment method, the wastewater is organic wastewater containing dimethylformamide. Therefore, dimethylformamide, a toxic chemical substance of which biological decomposition is relatively difficult, can be treated in an energy-saving manner by a biological treatment tank (for example, an aeration tank, catalytic oxidation tank or the like) having a submerged membrane and a foaming tank.
That is, when an operation for maintaining a high concentration of microorganisms by using the submerged membrane, organic wastewater containing dimethylformamide can be treated. Specifically, when an operation is performed so that the concentration in MLSS becomes 10000 ppm or higher, organic wastewater containing dimethylformamide can be treated.
At this time, a large amount of air is required, but, since micro air can be utilized to allow sludge to adhere to micro air and oxygen dissolution efficiency is improved by the micro air by using the foaming tank, organic wastewater containing dimethylformamide can be treated with low electrical energy. When a radial ring-shaped thread body is filled in a biological treatment tank, treatment of dimethylformamide is further stabilized and the treatment becomes more reliable.
In one embodiment of the present invention, the wastewater is organic wastewater containing dimethylformamide, ammonium fluoride and tetramethylammonium formade.
In the wastewater treatment method according to this embodiment, this mixed wastewater as a main component contains organic matter. Therefore, (1) dimethylformamide, (2) ammonium fluoride and (3) tetramethylammonium formade as toxic chemical substances, which are contained in wastewater actually discharged in a semiconductor factory and of which biological decomposition is relatively difficult, can be treated in an energy-saving manner by combination of an aeration tank or catalytic oxidation tank having a submerged membrane and a foaming tank.
In one embodiment of the present invention, the foaming tank is disposed above the biological treatment tank and has a foaming machine that rotates at a high speed so that an impeller generates bubbles.
According to the above embodiment, the foaming tank is disposed above the biological treatment tank. Therefore, since two water tanks (a foaming tank and a biological treatment tank) can be vertically disposed, an installation area can be saved and a space can be effectively utilized. Furthermore, wastewater which is introduced into the foaming tank is treated and then can be returned to the biological treatment tank (an aeration tank or catalytic oxidation tank) by gravity, which is useful for maintaining aerobicity. That is, micro air is returned to the original water tank without being separated from sludge.
Furthermore, since an impeller of a foaming machine rotates at a high speed, air is finely sheared and jetted into water, oxygen dissolution efficiency is improved, and a dissolved oxygen concentration in water can be increased. At the same time, air oxidation of organic matter contained in wastewater is accelerated by micro air.
In one embodiment of the present invention, an MLSS concentration of the returned sludge introduced into the foaming tank is 10000 ppm or higher.
In the wastewater treatment apparatus according to this embodiment, an MLSS (Mixed Liquor Suspended Solid) concentration of the returned sludge introduced into the foaming tank is made 10000 ppm or higher. Therefore, since the MLSS concentration in the biological treatment tank (for example, an aeration tank or catalytic oxidation tank) is 10000 ppm or higher, toxic chemical substances can be decomposed by an oxidizing ability of high-concentration aerobic microorganisms. Furthermore, it was found by experiments that air in the foaming tank became finer by making the MLSS concentration 10000 ppm or higher.
In one embodiment of the present invention, the biological treatment tank is an aeration tank or catalytic oxidation tank or a combination thereof, an upper portion of the aeration tank or catalytic oxidation tank is constituted by an aerobic portion, and a lower portion thereof is constituted by an anaerobic portion, and
wastewater is introduced from the lower portion into the biological treatment tank and wastewater is circulated in the biological treatment tank.
According to the wastewater treatment apparatus of this embodiment, an aeration tank or catalytic oxidation tank constituting a biological treatment tank consists of an upper portion, which is an aerobic portion, and a lower portion, which is an anaerobic portion. Therefore, while sludge generated in the upper portion, which is an aerobic portion, is digested in the lower portion, which is an anaerobic portion, organic matter can be decomposed. Therefore, genesis sludge capacity can be reduced in comparison with aerobic treatment only in the aerobic portion. Furthermore, since there are an aerobic process and an anaerobic process, wastewater is introduced from the lower portion of the biological treatment tank, and wastewater is circulated in the biological treatment tank, denitrification can be expected.
In one embodiment of the present invention, a submerged membrane is installed in the upper portion of the aeration tank or catalytic oxidation tank,
sludge transporting means is provided to introduce sludge in the anaerobic portion of the lower portion of the aeration tank or catalytic oxidation tank to the foaming tank, and
sludge is introduced from the foaming tank into the aerobic portion of the upper portion of the aeration tank or catalytic oxidation tank.
According to the wastewater treatment apparatus of this embodiment, in an anaerobic portion, which is a lower portion of an aeration tank or catalytic oxidation tank, highly adhesive sludge is introduced into an aerobic foaming tank by sludge transporting means in a short time. Therefore, while anaerobicity is maintained inside the sludge, micro air can adhere to a sludge surface, the sludge surface remains aerobic, and the sludge can be returned to the aerobic portion of the original aeration tank or catalytic oxidation tank and then to the anaerobic portion, which is the lower portion.
That is, treatment ability of anaerobic microorganisms and that of aerobic microorganisms are maintained with low electrical energy, and the sludge can be returned to the lower portion (anaerobic portion) of the original aeration tank or catalytic oxidation tank. According to this wastewater treatment apparatus, since aeration requiring high electrical energy (destruction by a large amount of air) is not necessary, a sludge mass is hardly destroyed.
In one embodiment of the present invention, sludge introduced into the foaming tank is:
sludge generated in a final part of a treatment process in the aeration tank or catalytic oxidation tank constituting the biological treatment tank, and
sludge from the foaming tank is introduced in an initial part of the treatment process in the aeration tank or catalytic oxidation tank.
According to the wastewater treatment apparatus of this embodiment, circulation in the whole aeration tank or catalytic oxidation tank can be made reliable, and a microorganism concentration in the tank can be averaged.
In one embodiment of the present invention, the biological treatment tank has at least a catalytic oxidation tank, a filler made of a radial ring form is filled in this catalytic oxidation tank, and
the submerged membrane in the aeration tank or catalytic oxidation tank constituting the biological treatment tank is an ultrafiltration membrane.
According to the wastewater treatment apparatus of this embodiment, since a filler is a radial ring form (aggregates of fibrous rings), a large amount of microorganisms can be propagated and immobilized thereon, and, as a result, treatment water quality can be stabilized. Furthermore, since the submerged membrane is an ultrafiltration membrane, propagated microorganisms can be maintained in the aeration tank or catalytic oxidation tank at a high concentration by performance of the ultrafiltration membrane, and thus toxic chemical substances can be treated by the microorganisms.
In one embodiment of the present invention, a material of the radial ring-shaped thread body is at least one of polyvinylidene chloride, polypropylene or vinylon.
According to the wastewater treatment apparatus of this embodiment, the radial ring form has practical strength and is not worn out at the same time. The radial ring form also has chemical resistance, and thereby does not need to be replaced even after a long-term use. That is, the filler has a long life.
In one embodiment of the present invention, the wastewater is wastewater containing toxic chemical substances.
According to the wastewater treatment apparatus of this embodiment, even when wastewater is wastewater containing toxic chemical substances, the toxic chemical substances can be treated by a wastewater treatment system having a microorganism concentration increased by a submerged membrane. Furthermore, since the foaming tank allows micro air to adhere to sludge, air can be efficiently utilized. Therefore, wastewater can be treated with low electrical energy, and thus an energy-saving system can be provided.
In one embodiment of the present invention, the wastewater is mixture wastewater of wastewater containing dimethylformamide and wastewater containing a developer.
According to the wastewater treatment apparatus of this embodiment, since a wastewater treatment system is a wastewater treatment system having a microorganism concentration increased by a submerged membrane, various kinds of toxic chemical substances can be treated. Therefore, wastewater containing dimethylformamide and wastewater containing a developer, which are generated in a semiconductor factory, can be treated in one water tank, and hence initial costs can be reduced in comparison with a case where separate wastewater treatment apparatuses therefor are constructed.
In one embodiment of the present invention, development wastewater is organic wastewater containing tetramethylammonium hydroxide.
According to the wastewater treatment apparatus of this embodiment, wastewater containing dimethylformamide and wastewater containing a developer including tetramethylammonium hydroxide (TMAH) as a main component, which are generated in a semiconductor factory, can be treated in one water tank, and hence initial costs can be reduced.